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arXiv · 2501.02122

Spiral Spin Liquid State in the Corrugated Honeycomb Lattice of CaMn$_2$P$_2$

Farhan Islam·Nikita D. Andriushin·Thaís V. Trevisan·Santanu Pakhira·Simon X. M. Riberolles·Zachary Morgan·Arianna Minelli·David C. Johnston·Robert J. McQueeney·Feng Ye·Peter P. Orth·David Vaknin
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Abstract

CaMn$_2$P$_2$ exemplifies the realization of a frustrated $J_1$-$J_2$-$J_3$ Heisenberg model of a corrugated honeycomb magnetic lattice. Previous studies show that below the N\'eel temperature ($T_{\rm N}$), the system forms a cycloidal $6\times 6$ $ab$-plane magnetic unit cell that conforms with various magnetic space groups. Here, we present single-crystal neutron-diffraction studies across expansive reciprocal-space volumes, confirming the cycloidal magnetic structure while uncovering further distinctive features. We find evidence for three magnetic domains, the analysis of which narrows the possible magnetic model structures. At $T_{\rm N}$, the insulator exhibits a sharp phase transition, above which the spin structure transforms into a spiral spin liquid state, evident via a continuous ring of scattering with degenerate wavevectors corresponding to a collection of short-range spiral spin configurations. These degenerate states emerge as thermal fluctuations effectively reduce the $J_3$ interaction. The integration of experimental, theoretical, and real-space simulation results reveals the intricate balance of exchange interactions ($J_1$-$J_2$-$J_3$) that stabilizes the ground-state magnetic structure and drives the emergence of a sought-after $U$(1)-symmetric spiral spin-liquid state with easy-plane anisotropy above the transition temperature.

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Farhan Islam, Nikita D. Andriushin, Thaís V. Trevisan, Santanu Pakhira, Simon X. M. Riberolles, Zachary Morgan, Arianna Minelli, David C. Johnston, Robert J. McQueeney, Feng Ye, Peter P. Orth, David Vaknin. 2025-01-03. Spiral Spin Liquid State in the Corrugated Honeycomb Lattice of CaMn$_2$P$_2$. https://arxiv.org/abs/2501.02122

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